1. Field of the Invention
This invention relates to a technique for imaging by detecting an interference light component of reflected light from an imaging object and reference light and particularly to a technique for imaging an imaging object carried in a carrier having optical transparency.
2. Description of the Related Art
In technical fields of medicine and biochemistry, samples carried in an appropriate carrier such as cells and microorganisms cultured in a container are observed. Techniques for imaging cells and the like using a microscope or the like are proposed as methods for observation without affecting the cells and the like to be observed. One of such techniques utilizes an optical coherence tomography technique. In this technique, low-coherence light emitted from a light source is caused to be incident as illumination light on an imaging object and interference light of reflected light (signal light) from the imaging object and reference light having a known optical path length is detected, whereby an intensity distribution in a depth direction of the reflected light from the imaging object is obtained for tomographic imaging. In this technique, reflected lights from a plurality of interfaces of the imaging object may be superimposed, thereby generating ghost-like image noise called self-correlation noise.
To deal with this problem, a shutter is provided in each of an optical path of return light from an object to be inspected and that of reference light, for example, in a technique described in JP 2010-038910A. By opening and closing these shutters if necessary, each of the return light and the reference light is singly detected and a self-correlation component of each is obtained. Further, a shutter mechanism for shutting off reflected light from an object is disclosed, for example, in International Publication No. 2013/136476, and this mechanism is described to remove image noise by software. This is supposed to cancel noise due to a self-correlation component of reference light.
If the cells and the like described above are an imaging object, imaging may be performed via a wall surface (e.g. bottom surface) of a carrier having optical transparency. In such a case, reflected light from the carrier wall surface is superimposed on a signal light, thereby acting similarly to reference light and image noise like a ghost image of the imaging object may appear at a depth different from the original one according to a distance between the wall surface and the imaging object. For such image noise, a process for removing the image noise ex-post facto is necessary in the above conventional technique and it cannot be dealt with in real time. Further, the reflected light from the wall surface and reflected light from the imaging object cannot be separated by opening and closing the shutters. Further, the above conventional technique has a complicated configuration in mechanism and operation such as because an optical system requires a movable mechanism and signal detection is necessary in each of an open state and a closed state of the shutter. Thus, it is desired to establish a technique capable of suppressing image noise due to reflected light from a carrier wall surface without complicating a configuration.